Are the Ibo people of Nigeria a lost tribe of Israel? A longstanding tradition among the Ibo says they are, and points to similarities in Ibo and Jewish cultures: a prescribed day of rest, circumcision (male, that is), the prohibition of pork. And now some Ibo have embraced Judaism, considering it the religion of their ancestors.

According to Jeff L. Lieberman’s uneven documentary “Re-emerging: The Jews of Nigeria,” the number of Jews there is small: fewer than 3,000. That’s hardly a tsunami in Africa’s most populous country, with more than 162 million people, or even among the Ibo, whose numbers have been estimated at anywhere from 20 million to 50 million, depending on the source. (Mr. Lieberman says 25 million.) The Ibo in the film are shown living Jewish lives, learning Hebrew, praying and reading Torah, and they are obviously sincere and committed. Their evident joy in Judaism is moving and unexpected.

Mr. Lieberman has a photogenic hero in the thoughtful Shmuel Tikvah Ben Yaacov (formerly Samuel Chukwuma), who grew up Roman Catholic but whose questioning led him to Judaism. His goal: to study at the Jewish Theological Seminary in Manhattan. His problem: a lack of money. (American and especially Israeli Jewish groups have not been quick to embrace the Ibo.)

“Re-emerging” can be pedestrian as filmmaking, though it remains interesting as long as it remains in Nigeria. But segments about African-Americans of Ibo descent belong in a different film, one about the Ibo diaspora. And Mr. Lieberman comically overreaches in suggesting that Nigeria’s tiny Jewish movement could have a large impact on black American life. Is ancestry necessarily destiny?